border-1px($color)
  position relative
  &:after
  	position absolute
  	display block
  	left 0
  	bottom 0
  	width 100%
  	border-top 1px solid $color
  	content ''

border-top-1px($color)
  position relative
  &:before
  	position absolute
  	display block
  	left 0px
  	top 0px
  	width 100%
  	border-bottom 1px solid $color
  	content ''

/**
 * 根据dpi显示不同的图片2x和3x
 */
bg-image($url)
  background-image url($url + '@2x.png');
  @media (-webkit-min-device-pixel-ration: 3),(min-device-pixel-ration: 3)
    background-image url($url + '@3x.png');
